The present invention relates to a system which uses magnetic induction to wirelessly transmit power and/or data through a barrier. More particularly, the invention relates to a method and apparatus for magnetically saturating the barrier to increase the power transfer efficiency of such a system.
Systems which use magnetic induction to wirelessly transmit power and data signals through barriers are known in the art. Referring to FIG. 1, such inductive power and data transfer systems commonly include a magnetic field transmitter 10 which is positioned on one side of a barrier 12 and a magnetic field receiver. 14 which is positioned on the opposite side of the barrier. The magnetic field transmitter 10 typically includes a transmitter coil 16 which is wound around a transmitter core 18 and the magnetic field receiver 14 usually includes a receiver coil 20 which is wound around a receiver core 22. The transmitter 10 is connected to a signal generator 24 which when activated generates a time varying current that flows through the transmitter coil 16. The flow of current through the transmitter coil 16 causes the transmitter core 18 to generate a time varying magnetic field which in theory flows through the barrier 12 to the receiver 14. At the receiver 14, the time varying magnetic field flows through the receiver core 22 and causes a current to flow through the receiver coil 20 which may then be used to power a device 26 that is connected to the receiver coil.
Although inductive data transfer systems work reasonably well with barriers made of many types of materials, inductive power transfer systems usually work satisfactorily only with barriers made of materials having relatively low magnetic permeabilities. The reason for this can be explained by reference to FIGS. 2 and 3, which are representations of the inductive power transfer system of FIG. 1 showing the paths that the magnetic field lines follow when the barrier 12 is made of a material having a relative magnetic permeability of around 10 and a material having a relative magnetic permeability of around 100, respectively. As shown in FIG. 2, when the barrier 12 is made of a material having a relative magnetic permeability of around 10, a substantial portion of the magnetic field lines generated by the transmitter 10 flow through the barrier and into the receiver core 22. In contrast, as shown in FIG. 3, when the barrier 12 is made of a material having a magnetic permeability of around 100, relatively few of the magnetic field lines flow through the barrier and into the receiver core 22. Instead, most of the magnetic field lines generated by the transmitter 10 “short” through the barrier 12 and return to the transmitter core 18 before reaching the receiver core 22.
The power transfer efficiency of an inductive power transfer system is directly proportional to the amount of magnetic flux generated by the transmitter which flows through the receiver core. The magnetic flux through the receiver core in turn is proportional to the number of magnetic field lines which pass through the transverse cross section of the receiver core. Comparing FIG. 2 with FIG. 3, therefore, one can see that the amount of magnetic flux in the receiver core 22 when the barrier 12 has a relative magnetic permeability of 10 is significantly greater than the amount of magnetic flux in the receiver core 22 when the barrier 12 has a relative magnetic permeability of 100. Therefore, the power transfer efficiency of the inductive power transfer system will be relatively high when the barrier 12 is made of a material having a relatively low magnetic permeability.
However, in many applications in which inductive power transfer systems would be beneficial, the barriers are made from materials having relatively high magnetic permeabilities. For example, in the subsea oil and gas production industry, electrically powered devices such as sensors, transmitters and actuators are sometimes positioned inside the production equipment components, such as wellhead housings, christmas tree flow lines and valve actuators, in order to monitor and control the flow of fluids through the components. Although power for these electrically powered devices may be provided by internal batteries or external power supplies, batteries lose charge over time and external power supplies require the drilling of holes through the components to accommodate pass-through connectors, and such holes are undesirable when the pressure integrity of the components must be assured.
Therefore, an inductive power transfer system for powering devices positioned inside subsea oil and gas production equipment components would be beneficial. However, many of the common materials used to manufacture these components, such as 4130, X65, Super Duplex and 1010 steel, have relative permeabilities near 1000. Consequently, the power transfer efficiencies for an inductive power transfer system for use with these components would likely be only a small fraction of a percent. As a result, inductive power transfer systems are not practical for use with such components.